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Journal of Luminescence

journal homepage: www.elsevier.com/locate/jlumin

Site occupation and 4f → 5d transitions of Ce3+ ions at mixed Ca2+/Y3+

sites in CaYAlO4: Insights from first-principles calculations

Jun Wena,b,∗, Guisheng Jianga, Jiyou Zhongc, Qingping Zhanga, Enjie Hed, Lixin Ningb,∗∗,Chang-Kui Duane,∗∗∗

a School of Physics and Electronic Engineering, Anqing Normal University, Anqing, 246133, ChinabAnhui Province Key Laboratory of Optoelectronic Materials Science and Technology, Anhui Normal University, Wuhu, 241000, Chinac School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou, 510006, Chinad School of Electrical and Electronic Engineering, Anhui Science and Technology University, Fengyang, 233100, Chinae Department of Physics, University of Science and Technology of China, Hefei, 230026, China

A R T I C L E I N F O

Keywords:Ce3+ ionsPhosphorsMixed occupationsDefect formation energies4f → 5d transitionsFirst-principles

A B S T R A C T

The first-principles calculations in the combination of hybrid density functional theory (DFT) and multi-configurational quantum-chemical methods are carried out to investigate geometric structures, electronicstructures and 4f → 5d transitions of Ce3+ ions at mixed Ca2+/Y3+ sites in the CaYAlO4 (CYAO). The mostenergetically stable unit cell among three nonequivalent configurations is firstly determined according to thetotal energies from DFT calculations. The calculated defect formation energies of lanthanide dopants andcomplexes in the host (with relatively stable configurations) then reveal the preferred substitution of Ce3+ ionsin the host. Moreover, the energies and relative oscillator strengths of the 4f → 5d transitions of Ce3+ at bothCa2+ and Y3+ sites are derived from the embedded-cluster quantum-chemical calculations at the CASSCF/CASPT2/RASSI−SO level. By comparison, the excitation bands in the experimental spectra of Ce3+-doped CYAOphosphors are mainly attributed to 4f → 5d transitions of Ce3+ ions at Ca2+ sites, which is well consistent withthe conclusions attained from the calculations on defect formation energies. The computational frameworkpresented in this study is beneficial to identify the occupation sites of lanthanide ions and assign the excitationbands of the experimental spectra for the phosphors with mixed sites or solid-solution structures.

1. Introduction

Ce3+-activated inorganic materials have received extensive atten-tion due to the electric-dipole-allowed 5d → 4f transitions, whichusually show wide and intense emissions and thus have a broad ap-plication in phosphor-converted white light-emitting diodes (pc-WLEDs) [1–13]. The 5d→ 4f electronic transitions of Ce3+ ions in hostsare strongly influenced by their coordination environments, because ofthe weak localization of 5d orbitals of Ce3+ ions and their intensecoupling with the lattice vibration. Among Ce3+-doped phosphors, thehosts with solid-solution structures or mixed occupation sites aregaining increasing attention, in consideration of the convenient ad-justment of spectroscopic properties of Ce3+ ions [9–13]. For examples,Brgoch et al. reported the efficient, thermally stable and blue-emittingborate phosphors (Ce3+-doped Ba2Y5B5O17 and Ba3Y2B6O15), in which

a part of crystallographically independent cation sites have a statisticalmixture of Y3+ and Ba2+ ions [9,10]. They also prepared the solidsolution compounds of the Ba2(Y1–xLux)5B5O17: Ce3+ (x=0, 0.25,0.50, 0.75 and 1), improving the photoluminescent quantum yield(PLQY), structural rigidity and thermal stability with the increase ofLu3+ ions [11]. As a significant supplement to experimental approaches(e.g. microstructural characterization, crystal structure analysis andspectroscopic measurement, and so on), the first-principles method wasoften performed on all the reasonable situations of occupation sites andlocal structures of lanthanide dopants in phosphors to obtain theirgeometric, electronic, thermodynamic and spectroscopic properties[14–22]. It thus makes quite possible the straightforward acquisition ofthe correlation between microstructures and macroscopic properties oflanthanide-doped phosphors.

In the present work, the CaYAlO4 (CYAO) host (with a mixed

https://doi.org/10.1016/j.jlumin.2019.116726Received 1 June 2019; Received in revised form 7 August 2019; Accepted 30 August 2019

∗ Corresponding author. School of Physics and Electronic Engineering, Anqing Normal University, Anqing, 246133, China.∗∗ Corresponding author.∗∗∗ Corresponding author.E-mail addresses: wenjunkd@mail.ustc.edu.cn (J. Wen), ninglx@mail.ahnu.edu.cn (L. Ning), ckduan@ustc.edu.cn (C.-K. Duan).

Journal of Luminescence 216 (2019) 116726

Available online 01 September 20190022-2313/ © 2019 Elsevier B.V. All rights reserved.

T

occupation of Ca2+ and Y3+ ions) [23–27] was chosen as the modelsystem to demonstrate the calculation framework of understanding therelationship of structure and properties for Ce3+-doped phosphors withmixed occupation sites or solid-solution structures. The first-principlescalculations combined with hybrid density functional theory (DFT) andwave function-based embedded cluster method are carried out in orderto investigate geometric structures, electronic structures and 4f → 5dtransitions of Ce3+ ions at mixed Ca2+/Y3+ sites in the CYAO. Themost stable configuration of the CYAO and further the occupationpreference of Ce3+ ions at Ca2+ and Y3+ sites in the host are de-termined by DFT geometric optimization calculations within the su-percell model. Then, the wave function-based embedded cluster cal-culations at the complete-active-space self-consistent field/complete-active-space second-order perturbation theory/restricted-active-spacestate-interaction spin-orbit (CASSCF/CASPT2/RASSI−SO) level[28–33] are performed to derive the 4f1 and 5 d1 energy levels of Ce3+

ions. According to the calculated results, the excited spectra of CYAO:Ce3+ phosphors are mainly ascribed to Ce3+ ions at Ca2+ sites with thecharge-compensating CaY defects. The presented calculations are ex-pected to improve our understanding of the differences of spectroscopicproperties of lanthanide ions at the mixed cation sites whose local co-ordination structures would change with the ratio of cations (such asCa2+/Y3+ in the CYAO).

2. Methods

The DFT calculations with hybrid functionals [34–37] (as im-plemented in VASP software [38,39]) were carried out to derive geo-metric and electronic structures of perfect and defective CYAO. Theprojected augmented wave (PAW) method [40] was adopted to de-scribe the interactions between ion cores and valence electrons, inwhich Ca 3s23p64s2, Y 4s24p65s24d, Al 3s23p, O 2s22p4, and Ce5s25p64f15d16s2 electrons were taken into account. The full atomicrelaxations of perfect unit cells and defective × ×2 2 2 2 1 supercells(with 112 or 111 atoms) were performed until that the change of thetotal energy is less than 10−5 eV and Hellman−Feynman forces onatoms become less than 0.01 eV/Å. The cut-off energy for the basis setof plane waves is set to be 520 eV. It is noted that × ×3 3 1 and

× ×7 7 2 k-point grids were used to sample Brillouin zones (BZs) forgeometry optimizations and electronic structure calculations of unitcells, respectively, while only one k-point (Γ point) was used for su-percells, due to the high calculation cost of hybrid functionals.

Using PBE0-calculated total energies of supercells, the formationenergy ( EΔ f ) of the defect D with the charge state q is calculated asfollows [41]:

∑= − − + +E D E D E n u q E εΔ [ ] [ ] [perfect] [ ]fq q

ii i Ftot tot VBM

(1)

where, E [perfect]tot and E D[ ]qtot are the calculated total energies of the

supercells of the perfect and defective CYAO, respectively. ni representsthe number of the atom of the element i, which is added to ( >n 0i ) orremoved from ( <n 0i ) the perfect × ×2 2 2 2 1 supercell. μi is theatomic chemical potential of the element i, and EF is the position of theFermi level relative to that of the valence band maximum (VBM) of thesystem (εVBM). In consideration of the reducing atmospheres (i.e., the O-poor conditions) in the preparation of samples, μCa, μY and μA1 areobtained from the calculated total energies per atom in the unit cell ofthe respective bulk materials, while μO is derived from the thermalequilibrium conditions of the CYAO, as follows:

+ + + =μ μ μ μ μ4Ca Y A1 O CaYA1O4 (2)

where, μCaYA1O4 is the total energy per formula unit of the CYAO. In thepresent work, −Kroger Vink notations were utilized to label defects,dopants and their complexes. The MX

q denotes that the atom M occupiesthe site of the atom X and meanwhile it possesses the charge state q. Inparticular, the VX

q represents the vacancy of the X (i.e., the absence of

the X at its site).The wave function-based ab-initio calculations at the CASSCF/

CASPT2/RASSI−SO level [28–33] as utilized in MOLCAS package [42]were performed on Ce3+-center clusters embedded into the hosts;whose geometric structures were obtained from PBE0 optimizationcalculations. The energies and relative oscillator strengths of the 4f →5d transitions of Ce3+ ions at both Ca2+ and Y3+ sites in the host werethen derived and compared with the experimental excitation spectra. Arelativistic effective core potential ([Kr] core) with a (14s10p10d8f3g)/[6s5p6d4f1g] Gaussian valence basis set was used for Ce [43], a [He]core effective core potential with a (5s6p1d)/[2s4p1d] valence basis setwas used for O [44]. The accurate quantum chemical calculations wereused to treat the valence electrons of the atoms in defective clusters,whose immediate lattice environments were described by the embed-ding ab-initio model potentials (AIMPs) [45] located at the host latticesites within a sphere with the radius of 10.0 Å. The point charges, whichwere situated at the lattice sites within a sphere shell with inner andexternal radii of 10.0 and 50.0 Å, respectively, were used to representthe lattice environments outside the AIMPs.

3. Results and discussion

The CYAO crystallizes in the tetragonal crystal system with thespace group of I4/mmm (No. 139). It belongs to the family of ABCO4

compounds, where A=alkaline-earth metals, B=rare-earth elements,and C=Al, Ga or transition metals. The unit cell of CYAO host containstwo calcium, two yttrium, two aluminum and eight oxygen ions, cor-responding to two chemical formulas of the CYAO. In its unit cell, four4e cation sites are occupied by two Ca2+ and two Y3+ ions, which aresurrounded by nine O2− ions. Two Al3+ ions take up six-coordinated 2asites, and O2− ions occupy four 4c and four 4e anion sites. Because ofthe random distribution for Ca2+ and Y3+ ions at 4e cation sites withthe occupation ratio of 1: 1, there are three types of nonequivalentconfigurations for the perfect unit cell, as illustrated in Fig. 1a–c (de-noted as configurations “1”, “2” and “3”, respectively). As shown inTable 1, DFT geometry optimization calculations with the PBE0 func-tional reveal that the configuration “3” is the most energetically stablestructure, with the energy advantages of 85 and 610meV than config-urations “2” and “1”, respectively. This complies well with the resultsfrom both HSE06 and PBE functionals. The configuration “3” would beemployed to construct initial structures of defective supercells, alongwith the geometries started from the configuration “2” for comparison.In the CYAO host (configuration “3”), the average bond lengths ofCa2+-O2- and Y3+-O2- are 2.569 and 2.462 Å, respectively, showing agood agreement with the trend of ionic radii of Ca2+ and Y3+ ions withnine coordination (1.180 and 1.075 Å, respectively [47]).

The total and orbital-projected density of states (DOSs) for the threenonequivalent configurations of the CYAO are calculated from both thePBE0 (as shown in Fig. 2a–c, respectively) and HSE06 functionals (asshown in Fig. 2d–f, respectively). One can find that the DOS patterns(Fig. 2a, b, 2d and 2e) of configurations “3” and “2” are similar, whilethose of the configuration “1” (Fig. 2c and f) are quite different. This isconsistent with the previous results of total energies of unit cells of thethree configurations, further confirming that the configuration “3” isthe most stable. From the figures, one can see that O-2p states pre-dominantly contribute to the top of valence band (VB), while thebottom of the conduction band (CB) is mainly made up of Ca-3d, Y-3dand O-2p states. The PBE0-and HSE06-calculated electronic band gap ofthe most stable configuration “3” of the CYAO is 5.57 and 4.80 eV,respectively. Sometimes, the electronic band gap of the host is esti-mated to be 1.08 times as much as the optical band gap according to therule of thumb [48], although the 1.08 proportionality factor is de-termined as the average of the limited available data [49,50]. On theother hand, the optical band gap is usually determined from the diffusereflectance spectra of the hosts by using the Kubelka-Munk method. InRef. [26], the optical band gap of Eu3+-doped CYAO phosphors

J. Wen, et al. Journal of Luminescence 216 (2019) 116726

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(containing 1mol% Eu3+) is determined as 4.23 eV by using the Ku-belka-Munk method, which is a little larger than the counterpart(4.09 eV) from the measured diffuse reflectance spectra of undopedCYAO powder in the present work (as shown in Fig. S1). It is found thatthe electronic band gaps of the CYAO calculated from hybrid func-tionals are much larger than the experimentally determined opticalband gaps. In addition, the PBE functional gives the CYAO (i.e., theconfiguration “3”) an electronic band gap of 3.22 eV, which is con-sistent with the fact that the conventional functional usually under-estimates the host band gap.

The radii of nine-coordinated Ce3+ ions are 1.196 Å, along withthose of 1.180, 1.075 and 0.535 Å for Ca2+ (nine coordination), Y3+

(nine coordination) and Al3+ ions (six coordination), respectively [47].Hence, Ce3+ ions in CYAO crystal ought to occupy Ca2+ and Y3+ ratherthan Al3+ sites. Various defects and impurities are ineluctably in-troduced into the host in order to compensate for the charge incon-sistency between lanthanide ions and host cations. According to pre-vious experiments [23–27], the precursors (such as CaCO3, Y2O3,Al2O3, SiO2 and lanthanide oxides) need to be calcined at high tem-peratures (more than 900 °C) under reducing atmospheres (such as 10%H2/90% N2 and 5% H2/95% Ar atmospheres). The intrinsic defects(such as CaY and YCa) instead of exogenous impurities (such as N and C)are supposed to play an important role in the charge compensation. ThePBE0-calculated formation energies EΔ f of neutral intrinsic defects inthe CYAO (originating from the configuration “3”) are presented inTable 2. The EΔ f of neutral cation vacancies are larger than 10.0 eV,indicating that they are not easy to generate in the CYAO preparedunder reducing atmospheres. In contrast, neutral oxygen vacancies arelikely produced under O-poor conditions in consideration of the small

EΔ f , which are 0.19, 0.72 and 0.41 eV for the vacancies at O2− sites inthe neighborhood of Y3+, Ca2+ and Al3+ ions, respectively. Besides,the single neutral antisite defects YCa, YAl and AlY seem to be easilygenerated in the host, with relatively smaller formation energies thanthose of the neutral CaY, CaAl and AlCa.

The defect formation energy of the complex ++ −Ce CaCa Y is only −20meV, although that of the single CaY

0 is relatively large, implying theunavoidable introduction of the charge-compensating defects in thehosts doped with Ce3+ ions. According to the calculated total energiesof supercells, lanthanide dopants and their charge-compensating de-fects tend to get close to each other, due to the Coulomb attraction oftheir opposite charges. The charge-compensating −CaY placed at thenearest site around the +CeCa was taken into account in this study,showing a smaller total energy of the supercell than the counterpart ofthose at non-nearest sites by more than 60meV. The differential chargedensities for ++ −Ce CaCa Y defect complex in the supercell of the CYAOare illustrated in Fig. 3a and b, with the projected view along the ne-gative a-axis and the negative c-axis, respectively. The isosurface levelsshow the charge transfer between +CeCa center and its ligands (the nineO2− and the −CaY), indicating the realization of the charge compensa-tion between Ce3+ and Ca2+ ions. The doped Ce3+ ions are introducedinto the host together with −CaY defects, showing the local disorderingpermutation of host cation ions (Ca2+ and Y3+) around the dopingCe3+ ions. From Table 2, it is found that Ce3+ ions prefer to occupylarger Ca2+ sites with the compensating Ca2+ ions at the nearest Y3+

sites around them, demonstrating an energy advantage of about 40meVthan the case of Ce3+ ions occupying Y3+ sites. Moreover, the forma-tion energies of both ++ −Ce CaCa Y and CeY

0 would increase by more than800meV, when the configuration “2” was utilized as the originalstructure of defective supercells, further showing the energetic stabilityof the configuration “3”.

Based on DFT-optimized crystal structures, (CeCaO9)15− and(CeYO9)15− defective clusters embedded into the CYAO host werefirstly constructed to simulate coordination structures around Ce3+

ions. Then, the quantum-chemical ab-initio calculations at the CASSCF/CASPT2/RASSI−SO level were performed on the embedded clusters toderive the energies and oscillator strengths of the 4f → 5d transitions ofCe3+ ions in the host. In Table 3, the energies of the 4f → 5d transitionsof Ce3+ ions at Ca2+ and Y3+ sites in the supercell of the CYAO(configurations “3”) are provided along with the experimental values.One can find that the centroids ( EΔ ced) of the calculated 5d crystal fieldenergy levels of Ce3+ ions (38926 and 37933 cm−1 for ++ −Ce CaCa Y andCaY

0 centers, respectively) are in a good agreement with the experi-mental one (of 36899 cm−1). The crystal filed splitting ( EΔ cfs) of the 5denergy levels of ++ −Ce CaCa Y complexes (with the value of 20610 cm−1)

Fig. 1. The schematic diagrams of three nonequivalent configurations (a) “1”, (b) “2” and (c) “3” of the unit cell of the CYAO.

Table 1DFT-calculated lattice parameters and relative total energies of the unit cells ofthree nonequivalent configurations for the CYAO.

Cases Methods a (Å) b (Å) c (Å) α= β= γ Relative totalenergy (meV)

“1” PBE0 3.648 3.648 11.858 90° 610“2” PBE0 3.640 3.640 11.819 90° 85“3” PBE0 3.620 3.620 12.061 90° 0“1” HSE06 3.648 3.648 11.864 90° 612“2” HSE06 3.641 3.641 11.820 90° 93“3” HSE06 3.621 3.621 12.065 90° 0“1” PBE 3.688 3.688 11.929 90° 556“2” PBE 3.680 3.680 11.897 90° 95“3” PBE 3.657 3.657 12.151 90° 0Exptl. [46] – 3.645 3.645 11.874 90° –

J. Wen, et al. Journal of Luminescence 216 (2019) 116726

3

is close to the experimental one of 20297 cm−1, while the counterpartfor CeY

0 centers differs greatly from the experimental one. Moreover,calculated schematic diagrams for the energies and relative oscillatorstrengths of 4f1 → 5di (i=1–5) transitions of Ce3+ ions at both Ca2+

and Y3+ sites in the CYAO (configurations “3”) are illustrated in Fig. 4a

and b, respectively, along with the experimental excitation spectrum[24]. By comparison, we conclude that the excitation spectrum of Ce3+-doped CYAO phosphors are mainly attributed to the 4f → 5d transitionsof Ce3+ ions at Ca2+ sites in the CYAO (configuration “3”), togetherwith the subordinate contribution of the 4f → 5d transitions of Ce3+

ions at Y3+ sites. In particular, the first two excitation bands with thepeak values of 27322 and 33445 cm−1 in the spectrum are ascribed tothe 4f1 → 5d1 and the 4f1 → 5d2, 3 transitions of ++ −Ce CaCa Y centers,respectively. The band above 45000 cm−1 is mainly attributed to the4f1 → 5d4, 5 transitions of ++ −Ce CaCa Y centers. Besides, the weak ex-citation band in the range of 37500 and 45000 cm−1 may be related to4f1 → 5d2-5 transitions of CeY

0 centers. Noted that the 4f1 → 5d tran-sitions of Ce3+ ions in the case originated from the configuration “2”unlikely contribute to the excitation bands in the experimental spectra,in consideration of much larger defect formation energies.

Fig. 2. Total and orbital-projected DOSs for unit cells of configurations (a) “3”, (b) “2” and (c) “1” of the CYAO derived from the standard PBE0 functional with a× ×7 7 2 k-point grid to sample the Brillouin zone, and the counterparts of configurations (d) “3”, (e) “2” and (f) “1” from the HSE06 hybrid functional.

Table 2Defect formation energies EΔ f from PBE0-calculated total energies of supercellsfor neutral defects and defect complexes in the CYAO (configuration “3”).

Energy CaY0 YCa

0 A1Y0 YA1

0 CaA10 A1Ca

0 VO10

ΔEf (eV) 4.22 0.60 2.90 2.54 6.79 4.35 0.19Energy VO2

0 VO30 VCa

0 VY0 VA1

0 ++ −Ce CaCa Y CeY0

ΔEf (eV) 0.72 0.41 10.14 13.38 13.02 −0.02 0.02

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4. Conclusions

In the present work, the geometric structures, electronic propertiesand optical transitions of Ce3+ ions in the CYAO are studied by meansof the combination of DFT calculations with hybrid functionals andembedded-cluster ab-initio calculations at the CASSCF/CASPT2/RASSI-SO level. The DFT geometry optimization calculations (with PBE,HSE06 and PBE0 functionals) demonstrate that the configuration “3” ofthe unit cell (in which Ca2+ and Y3+ ions randomly occupy 4e cationsites with the ratio of 1: 1) is the most energetically stable. Then, it isfound from PBE0-calculated defect formation energies that Ce3+ ionsseem to prefer to substitute large Ca2+ instead of Y3+ ions, with theenergy advantages of 40meV. Moreover, the experimental excitationspectra of Ce3+-doped CYAO phosphors are successfully assigned, ac-cording to the calculated energies and relative oscillator strengths ofthe 4f → 5d transitions of Ce3+ ions (at both Ca2+ and Y3+ sites). Onecan find that the first two excitation bands with the peak values of27322 and 33445 cm−1 in the experimental spectra of CYAO: Ce3+

phosphors are ascribed to 4f1 → 5d1 and 4f1 → 5d2, 3 transitions of++ −Ce CaCa Y complexes, respectively, and the band above 45000 cm−1 is

mainly attributed to the 4f1 → 5d4,5 transitions of ++ −Ce CaCa Y com-plexes. Besides, the obtained HRBE scheme of the 4f1 and 5d1 states ofLn3+ and Ln2+ ions at Ca2+ sites in the CYAO would be beneficial toinvestigate luminescent properties of lanthanide ions in the same host.The presented calculations combined the hybrid DFT with the multi-configurational ab-initio method may be utilized for Ce3+-dopedphosphors in order to determine luminescent centers and reveal thedistinctions of spectroscopic properties of mixed cation sites with thedifferent sort orders of cations in hosts.

Acknowledgments

Funding supports from National Natural Science Foundation ofChina (Grant Nos. 11604002, 11974022, 61635012, 11705003 and51702057), National Key Research and Development Program of China(Grant No. 2016YFB0701001), Open Project Fund of Anhui ProvinceKey Laboratory of Optoelectronic Materials Science and Technology(Grant No. OMST201704) and Natural Science Foundation of AnhuiProvince (Grant No. 1808085MA09) are gratefully acknowledged. JunWen also acknowledges the Project of Support Program for ExcellentYoung Talents in Colleges and Universities of Anhui Province (GrantNo. gxyqZD2019046) as well as the Supercomputing Center ofUniversity of Science and Technology of China.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://

Fig. 3. Differential charge density for ++ −Ce CaCa Y defect complex in the supercell of the CYAO (configuration “3”): projected view along (a) the negative a-axis and(b) the negative c-axis. The isosurface levels for differential charge density are 0.007 e/Bohr3 (yellow) and −0.007 e/Bohr3 (blue).

Table 3Calculated energies (in unit of cm−1) of 4f1 and 5 d1 levels for Ce3+ ions atCa2+ and Y3+ sites in the CYAO (configuration “3”) by using the CASSCF/CASPT2/RASSI‒SO method. It is noted that the experimental values in the tablecorrespond to the positions of the peaks of excitation bands in the experimentalspectra of Ce3+-doped CYAO phosphors [24,25].

Levels Configuration “3” Exptl [25] Exptl [24]

++ −Ce CaCa Y CaY0

4f1 0 04f2 502 3074f3 716 3954f4 2453 22574f5 2636 23574f6 3196 25794f7 3537 27835d1 29137 30602 28169 273225d2 32929 37280 334455d3 34072 38404 354615d4 48744 40105 406505d5 49747 43272 47619ΔEced 38926 37933 36899ΔEcfs 20610 12670 20297

Fig. 4. Schematic diagram for the calculated energies and relative oscillatorstrengths of 4f1 → 5di (i=1–5) transitions of (a) ++ −Ce CaCa Y and (b)7 CeY

0

centers in the CYAO (configuration “3”), along with (c) the experimental ex-citation spectrum [24].

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doi.org/10.1016/j.jlumin.2019.116726.

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